I recently just bought my 1st dslr (40d 28-135mm f/3.5-5.6). Now im pretty familiar with how iso, aperture, shutter speed all effect the exposure. My question has to do with the lenses. Does the "f/3.5-5.6" represent the min-max aperture you can use with that particular lens? If not what exactly do those #'s mean? Also what does it mean when someone says they need a slower or faster lens and how does that effect the pictures taking prosess? Thanks for the help!!